The present invention relates to a process and new sorbents for selective adsorption and recovery of alkenes from gaseous mixtures containing the alkenes.
Several methods are known for the separation of selected organics from gaseous mixtures. These include, for example, cryogenic distillation, liquid adsorption, membrane separation and pressure swing adsorption in which adsorption occurs at a higher pressure than the pressure at which the adsorbent is regenerated. In an analogous method, temperature swing adsorption is used in which adsorption occurs at a lower temperature than the temperature at which the adsorbent is regenerated. In these adsorption techniques, after adsorption occurs, release of the adsorbed material is achieved by either decreasing the pressure or raising the temperature. Of these methods, cryogenic distillation and liquid adsorption represent commonly known methods for separating selected organics from gaseous mixtures. Cryogenic distillation has been used for over sixty years for separation. However, it is very energy intensive and difficult to accomplish because of relatively close volatilities when alkene\alkane (olefin\paraffin) separation is required. For example, ethane\ethylene separation is carried out at about −25° C. and 320 psig (2.603 MPa) in a column containing over 100 trays, and propane\propylene separation is performed by an equally energy-intensive distillation at about −30° C. and 30 psig (0.308 MPa). It is evident that high capital costs and high operational costs are incurred in any cryogenic distillation approach. Early attempts were made to use liquid solutions for separation by means of metallic ions dispersed in solution. Such methods are very difficult to conduct and not easily adaptable to commercial use.
More recently, molecular sieve zeolites have been investigated to selectively adsorb carbon monoxide and hydrocarbons from gaseous mixtures. However, these zeolites have shown only moderate capacity for recovery of the targeted compound to be adsorbed. An example is adsorption on cuprous ion exchange y-type zeolites (U.S. Pat. Nos. 4,717,398 and 5,365,011). Presently, many of the available adsorbents known for other uses, such as carbon monoxide removal, do not have selectivities for olefins as demonstrated by the aforesaid '398 and '011. Therefore, what is needed are new adsorbents (sorbents) effective for olefin/paraffin separation.